dangers in changing trans fluid in an old transmission?
 

So generally i'm a clean fluids kind of guy...
I've heard from a few people that new fluid in an old transmission can cause failure... The best explanation for this that i heard was that new fluid, having stronger detergent properties than old fluid can attack the clutch materials in the old transmission.
I have an 85 300d i just purchased. it runs well, transmission seems to shift well (a bit of a hard shift when cold, but that seems normal) 143,000 miles. I have no idea when the fluid was last changed. It is pink on the dipstick. If this transmission pops the car is getting parted out... i'm a student, i can't do a transmission right now.
So should i risk fluid and a filter? I basically need this thing to last me about 2-3 years. 40,000 more miles maybe?

is there any preferred fluid for an old possibly neglected car such as this?

Pure B S....
Several threads in the archives should have put this to rest long ago..
perhaps search ' Larry Bible ' ' magic fluid '.....

The reason it started was people putting ' temporal incident ' into the ' causational incident ' category...
Many times trans are not serviced until way late... certainly not at their recommended frequency...which is pretty short for the MB compared to old American cars...
so they change it....and just due to the age of the trans and lack of care.... pretty soon it gives up the ghost... but they blame the fluid and filter change....because they are not very bright...

The regular approved fluid with two cans of Trans-X is what I use in all new to me auto trans cars..... follow directions on side of can...and do search in archives about it... simply a varnish desolver...
Then change the fluid and filter again soon....like 100 miles.... since you do not know the history of the maintenance....

That's interesting. Last week I took my 2002 Lexus to a Texaco Oil Change shop for an oil change. They wanted to change the transmission fluid, talked to me about it, then refused to do it because I could not provide evidence that it had been changed 40K miles ago. They said they had had problems after changing the fluid in trannies that had not been changed per manufacturer recommendations. Said sometimes the tranny refused to shift properly with the new fluid.

So I am wondering - urban myth or not?

Well, Here is the statement from JIMSMITH.. mod and trusted engineer...from 2003 no less...

""Dirt, varnish, burned transmission fluid by products and other foriegn materials are not included when the transmission is built at the factory, and any transmission relying on the accumulation of these foriegn materials in strategically important locations to operate is already broken."" --JimSmith

from :
http://www.peachparts.com/shopforum/diesel-discussion/82890-flush-not-flush-question.html?highlight=magic

Working for Texaco does not make one immune to urban myths....

I've had a couple of folks who are experienced servicing/rebuilding US transmissions say that it's not necessary to change it as long as it looks good. Trouble is, if it looks cruddy then you have problems already.

May be a causation/correlation thing?

It's BS. Click and Clack summed up this well one day. You only hear about the one guy that changed his fluid and the trans went south. You never hear about the other 100,000 people that changed there's with no change or positive benefits. We like to remember the bad stuff. If the trans failed it was already on it's way out.

Changing the fluid is never a bad idea. The old fluid is full of metal bits that abrade everything and wear it all out. It's always good to get that fluid out and putting fresh in as well as a filter. I second the Trans-X. I've seen good results putting it in my 82 wagons trans. Put a bottle in before you refill the system. Then fill the rest with ATF.

alright i'll add it back to the project list.

Not disagreeing, just giving personal experience. Never used Trans X. What does it do? Something like the old engine honey stuff (cannot remember the name) that we used to put in the old gassers oil in the '60's? Not Bardahl but something like it.

The fact is you don't know when your tanny was last serviced. It's fine to have a "pop" on the shift because that means things are ok... if pop is a firm shift. It also may mean that you may have a vacuum issue.

So, if you are going to change the filter keep your the oil you drain in a clean container. Once you have replaced the filter and sealed the tranny refill everything. When you refill, which should be almost exactly 4qts. use about 1.5 quarts of the old tranny fluid. It's a safety precaution, and anyone that wants to argue why is welcome to argue it , but I am not going to discuss why right now.

You should be fine all in all even if you replace all the old fluid. On these cars, from what I know from experience, most of the time, when the reverse goes out is when you should have feelings of despair.

In the worst case, drive it until it cannot be driven.

From post number two :

"simply a varnish desolver..."---leathermang

Pure Bull **** !
No Wonder you ' are not going to discuss why right now ' ...
What a cop out... the truth is you have no facts to support your statement and it should be excised from the thread.

Ya, what is putting some of the old fluid back in going to accomplish? Putting dislodged dirt back in for that nice self-polishing effect? :confused:

-J

Well put... some of the same people...not many... two or three regularly post things like this even after good references ( like to JimSmith's post ) have been put up... I often wonder if they just do it to get a reaction... and not because they really believe it to be true....

There are antibodies in the old fluid which MUST be transferred with the new or your transmissions immune system will be compromised.

Simply put, if you don't do this your transmission could get sick.

:D